/*
 * [New BSD License]
 * Copyright (c) 2011-2012, Brackit Project Team <info@brackit.org>  
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the Brackit Project Team nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.brackit.xquery.compiler.optimizer.walker.topdown;

import org.brackit.xquery.compiler.AST;
import org.brackit.xquery.compiler.XQ;
import org.brackit.xquery.compiler.optimizer.walker.Walker;

/**
 * @author Sebastian Baechle
 * 
 */
public class LeftJoinUnnesting extends Walker {

	@Override
	protected AST visit(AST join) {
		if ((join.getType() != XQ.Join) || (!join.checkProperty("leftJoin"))) {
			return join;
		}
		AST parentJoin = join.getParent().getParent();
		if ((parentJoin.getType() != XQ.Join)
				|| (join.getParent().getChildIndex() != 1)) {
			return join;
		}
		
		AST anc = parentJoin.getParent();
		anc.replaceChild(parentJoin.getChildIndex(), join);
		AST out = join.getLastChild();
		join.replaceChild(3, parentJoin);
		parentJoin.getChild(1).replaceChild(0, out);
		
		return anc;
	}
}
